The present disclosure relates to a motor-driven Roots pump.
The housing of a motor-driven Roots pump rotationally supports a drive shaft and a driven shaft. The drive shaft and the driven shaft are arranged parallel to each other. The drive shaft is rotated through the driving of an electric motor. A drive gear is fixed to the drive shaft. A driven gear is fixed to the driven shaft and meshed with the drive gear. The drive shaft has a drive rotor and the driven shaft has a driven rotor. The driven rotor is meshed with the drive rotor. As the drive shaft is rotated through the driving of the electric motor, the driven shaft is rotated reversely with respect to the drive shaft through the drive gear and the driven gear, which are meshed with each other. The drive rotor and the driven rotor, which are meshed with each other, are thus rotated in mutually different directions. This allows the motor-driven Roots pump to selectively draw and discharge fluid.
A motor chamber, a gear chamber, and a rotor chamber are formed in the housing. The motor chamber accommodates the electric motor. The gear chamber accommodates the drive gear and the driven gear. The rotor chamber accommodates the drive rotor and the driven rotor. Oil is received in the gear chamber in a sealed manner to lubricate the drive gear and the driven gear and limit a temperature rise. The drive gear and the driven gear are thus dipped in the oil and rotated. This allows for high-speed rotation of the drive gear and the driven gear without causing seizure or wear.
For example, a Roots pump described in Japanese Laid-Open Patent Publication No. 2006-283664 has a motor chamber, a gear chamber, and a rotor chamber in this order along the rotational axis of the drive shaft. The housing of the Roots pump has a first partition wall to separate the gear chamber from the motor chamber in the direction of the rotational axis of the drive shaft. The first partition wall has a first seal accommodating recess to accommodate an annular first seal member. The drive shaft extends through the first seal member. The first seal member seals the gear chamber and the motor chamber from each other. The first seal member prevents oil leakage from the gear chamber into the motor chamber through the first seal accommodating recess. The housing also has a second partition wall to separate the gear chamber from the rotor chamber in the direction of the rotational axis of the drive shaft. The second partition wall has a second seal accommodating recess to accommodate an annular second seal member. The drive shaft extends through the second seal member. The second seal member seals the gear chamber and the rotor chamber from each other. The second seal member prevents oil leakage from the gear chamber into the rotor chamber through the second seal accommodating recess. The second partition wall also has a third seal accommodating recess to accommodate an annular third seal member. The driven shaft extends through the third seal member. The third seal member seals the gear chamber and the rotor chamber from each other. The third seal member prevents oil leakage from the gear chamber into the rotor chamber through the third seal accommodating recess.
If, for example, the level of oil in the gear chamber is located in the vicinity of the rotational axes of the drive shaft and the driven shaft, the first seal member, the second seal member, and the third seal member are partially immersed in the oil in the gear chamber. This lubricates the first seal member, the second seal member, and the third seal member and limits a temperature rise.
When the motor-driven Roots pump is operated, the drive gear and the driven gear rotate while stirring up oil in the gear chamber. If, at this time, the level of oil in the gear chamber is located in the vicinitie of the rotational axes of the drive shaft and the driven shaft, the resistance to stirring of the drive gear and the driven gear increases. The electric power consumed by the electric motor is thus increased. However, if a smaller amount of oil is received in the gear chamber, the oil supply to the first seal member, the second seal member, and the third seal member is hampered.